Vertical field effect transistors

ABSTRACT

Vertical field effect transistors (FETs) with minimum pitch and methods of manufacture are disclosed. The structure includes at least one vertical fin structure and gate material contacting with the at least one vertical fin structure. The structure further includes metal material in electrical contact with the ends of the at least one vertical fin.

FIELD OF THE INVENTION

The invention relates to semiconductor structures and, moreparticularly, to vertical field effect transistors (FETs) with minimumpitch and methods of manufacture.

BACKGROUND

A vertical field-effect transistor (FET) has a channel perpendicular tothe substrate surface, as opposed to being situated along the plane ofthe surface of the substrate. By using this design, it is possible toincrease packing density. That is, by having the channel perpendicularto the substrate surface, vertical FETs improve the scaling limit beyondplanar finFETs.

However, vertical FETs are still severely challenged past the 7 nm nodedue to high aspect ratios, Vmax limits, and material thickness notscaling well. For example, insulator material and shared contacts formedbetween gate material of adjacent vertical FETs make it very difficultto scale the devices beyond the 7 nm node, basically due to materialthicknesses, leakage concerns, breakdown voltage, decreased resistancesand capacitance, etc. Accordingly, these constraints make it verydifficult to decrease gate pitch in current vertical FET designs.

SUMMARY

In an aspect of the invention, a structure comprises at least onevertical fin structure and gate material contacting with the at leastone vertical fin structure. The structure further comprising metalmaterial in electrical contact with the ends of the at least onevertical fin.

In an aspect of the invention, a structure comprises: at least twoadjacent fin structures of semiconductor material with a source regionand a drain region at opposing ends; gate material about the twoadjacent fin structures and between the opposing ends; a space betweenthe gate material of the two adjacent fin structures; and drain contactsand source contacts at the opposing ends of the two adjacent finstructures on the source region and the drain region.

In an aspect of the invention, a method comprises: forming at least onevertical fin structure; forming gate material contacting with the atleast one vertical fin structure; and forming source and drain contactsat ends of the at least one vertical fin structure by deposition ofmetal material in electrical contact with the silicide regions.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIG. 1 shows a respective structure and fabrication processes of formingfins according to aspects of the invention;

FIG. 2 shows a structure and respective fabrication processes of formingdielectric material between fins according to aspects of the invention;

FIG. 3 shows a structure and respective fabrication processes of forminggate material around the fins according to aspects of the invention;

FIG. 4 shows a structure and respective fabrication processes ofpatterning the gate material according to aspects of the invention;

FIG. 5 shows a structure and respective fabrication processes of formingdielectric material about vertical gate structures according to aspectsof the invention;

FIG. 6 shows a structure and respective fabrication processes of formingepitaxial material on exposed portions of fins according to aspects ofthe invention;

FIG. 7 shows a structure and respective fabrication processes of formingof silicide regions according to aspects of the invention;

FIG. 8 shows a structure and respective fabrication processes of formingcontact regions according to aspects of the invention;

FIGS. 9a and 9b show cross-sectional and top-down views of analternative structure and respective fabrication processes according toaspects of the invention;

FIGS. 10a and 10b show cross-sectional and top-down views of anotheralternative structure and respective fabrication processes according toaspects of the invention;

FIGS. 11a and 11b show cross-sectional and top-down views of anotheralternative structure and respective fabrication processes according toaspects of the invention; and

FIG. 12 shows another alternative structure and respective fabricationprocesses according to aspects of the invention.

DETAILED DESCRIPTION

The invention relates to semiconductor structures and, moreparticularly, to vertical field effect transistors (FETs) with minimumpitch and methods of manufacture. More specifically, the vertical FETsof the present invention have the source/drain contacts formed at endsof the gate structures (compared to between the gate structures) inorder to reduce the pitch between adjacent gate structures, e.g.,vertical FETs. Advantageously, by moving the source/drain contact to theoutside ends of the FETs, the pitch of the FETs can be scaledsignificantly. Also, gate to contact capacitance is significantlyreduced by moving the source/drain contacts to the outside ends of theFETs.

Vertical FETs significantly improve the scaling limit beyond planarfinFETs; however, conventional vertical FETs are still severelychallenged past the approximately 7 nm node due to high aspect ratios,Vmax limits, and material thickness not scaling well. For example, incurrent layouts the source and drain contact(s) are placed betweenadjacent FETs due to resistance issues. The challenge is that as thepitch is scaled the width (thickness) of the contact decreases. Thisresults in a high overall contact resistance. This also results in veryhigh contact to gate capacitance and lack of pitch scaling. That is, theplacement of the contact between the gate structures effectively limitsthe scaling properties between adjacent vertical FETs, limiting thepitch to about 27 nm.

In comparison, the vertical FETs of the present invention have contactsat the ends of the gate structures. By placing a shared contact (orsource/drain contacts) at ends of the FET and making the FET conductorbottoms tall, the resistance issues are reduced while providing lowercontact to gate capacitance and, importantly, the ability to scale thegate pitch, e.g., space between adjacent FETs. Effectively, eliminatingthe contact between the metal gate structures of the vertical FETs alsoeliminates a layer of insulator material, thereby making it possible tosignificantly decrease the pitch (spacing) between adjacent verticalFETs. In fact, the scaling can be improved by approximately 20% orgreater (e.g., approximately 29% in some instances) compared toconventional structures which place source and drain contact(s) betweenadjacent FETs. Moreover, by removing the shared contact between themetal gate structures, it is also possible to provide an air gap betweenthe adjacent FETs effectively reducing capacitance.

In embodiments, the vertical FETs can be single or double sided gates.In addition, the vertical gate structures can be long without increasingpitch, and gate width, fin thickness and insulator materials can all bescaled accordingly. In this way, it is possible to minimize or scale thepitch between adjacent vertical FETs, by forming the contacts at theirends. In further embodiments, the vertical FETs comprise a firstvertical double gate CMOS FET pair having a shared contact strap at oneor both ends (source and drain regions) of the FINFET between theadjacent pair of FETs and a shared or individual S/D silicide region(silicide at shared S/D region). An air-gap can be formed between theadjacent vertical FETs, with a high aspect ratio bottom contact regionfor low horizontal resistance.

The vertical FETs of the present invention can be manufactured in anumber of ways using a number of different tools. In general, though,the methodologies and tools are used to form structures with dimensionsin the micrometer and nanometer scale. The methodologies, i.e.,technologies, employed to manufacture the vertical FETs have beenadopted from integrated circuit (IC) technology. For example, thevertical FETs are built on wafers and are realized in films of materialpatterned by photolithographic processes on the top of a wafer. Inparticular, the fabrication of the vertical FETs uses three basicbuilding blocks: (i) deposition of thin films of material on asubstrate, (ii) applying a patterned mask on top of the films byphotolithographic imaging, and (iii) etching the films selectively tothe mask.

FIG. 1 shows a beginning structure and respective processing steps inaccordance with aspects of the present invention. The structure 10includes a substrate 12 and an insulator layer 14 formed thereon. Inembodiments, fins 16 are formed on the insulator layer 14 usingconventional lithography and etching steps. In embodiments, theinsulator layer 14 can be a buried oxide layer (BOX) and the fins 16 canbe formed from silicon on insulator material (e.g., SOI) or anysemiconductor material including, but not limited to, Si, SiGe, SiGeC,SiC, GE alloys, GaAs, InAs, InP, and other III/V or II/VI compoundsemiconductors.

In embodiments, the fins 16 are formed by two etching processes. Forexample, the first etching process forms the lower portion 16 a of thefins 16, which is wider than the narrower portion (body) 16 b of thefins 16; whereas, the second etching process forms the narrower portion(body) 16 b of the fin 16. In any of the embodiments described herein,the bottom region, e.g., wide portion 16 a of the fin 16 can be madesignificantly taller, e.g., 30 nm, than conventional structures therebyfurther reducing resistance.

By way of example of forming the fins 16, the first etching process canbe a sidewall image transfer (SIT) technique. In the SIT technique, amandrel material, e.g., oxide or nitride material, is formed on thesemiconductor material using conventional deposition, lithography andetching processes. In an example of a SIT technique, the mandrelmaterial can be deposited using conventional CVD processes. A resist isformed on the mandrel material, and exposed to light to form a pattern(openings). A reactive ion etching (RIE) is performed through theopenings to form the mandrels. Spacers are formed on the sidewalls ofthe mandrels which are preferably material that is different than themandrels, and which are formed using conventional deposition processesknown to those of skill in the art. The spacers can have a width whichmatches the dimensions of the lower portion 16 a of the fins 16, forexample, e.g., about 7 nm. The mandrels are removed or stripped using aconventional etching process, selective to the mandrel material. Anetching is then performed within the spacing of the spacers to form thesub-lithographic features. The sidewall spacers can then be stripped. Inembodiments, the narrower fin portions (e.g., body) 16 b of the fins 16can be formed after the patterning process of the wider portion 16 a,using conventional patterning processes as contemplated by the presentinvention. In embodiments, the narrower fin portions 16 b can beapproximately 5 nm or less.

As shown in FIG. 2, a dielectric material 18 is deposited on the fins16, and etched back to expose the vertical portions of the fins 16,e.g., the narrower fin portions (e.g., body) 16 b of the fins 16. Inembodiments, the dielectric material 18 will protect the lower portion16 a of the fins 16 during subsequent gate formation and will ensurethat a later formed source or drain portion formed at this wider portionof the fin will not short to a gate structure. The dielectric material18 can be an oxide material, which can be blanket deposited over thefins 16 and on any exposed surfaces of the structure by using aconventional deposition process. For example, the deposition process canbe a chemical vapor deposition (CVD) process.

In FIG. 3, a gate dielectric material 20 and a gate material 22 areformed over the fins 16, e.g., the narrower fin portions (e.g., body) 16b of the fins 16, and on the etched back dielectric material 18. Inembodiments, the gate dielectric material 20 can be a high-k materialsuch as a hafnium based material, e.g., hafnium oxide. The gate material22 can be any appropriate metal material or combinations of metalmaterials, depending on the desired workfunction properties. Inembodiments, the gate dielectric material 20 and the gate material 22have a thickness of about 5 nm or less, and wrap around the entireexposed vertical surfaces of the fins 16 (e.g., narrow portion 16 b), ontop of the dielectric material 18. The gate dielectric material 20 andthe gate material 22 can be formed by a conventional deposition process,e.g., CVD, followed by a recessing process such that the verticalextents of the narrower fin portions (e.g., body) 16 b of the fins 16are exposed. In embodiments, the recess process can be a chemicalmechanical process (CMP), which exposes a top surface of the fin 16following by an etch back process.

In FIG. 4, the gate dielectric material 20 and the gate material 22 areetched back, forming a space 24 between adjacent gate structures 10′. Inembodiments, the space 24 between the gate dielectric material 20 andthe gate material 22 can be formed by conventional lithography andetching processes, e.g., reactive ion etching (RIE) processes. The space24 can be about 6 nm or less and is capable of being further scaled. Inembodiments, the recessing of the gate dielectric material 20 and thegate material 22 can also be performed prior to or after spaceformation.

As shown in FIG. 5, a dielectric material 26 is formed within the spacebetween the adjacent structures 10′, and on any exposed vertical extentof the narrow portion 16 b of the fin 16, resulted from the etch backprocess of the gate dielectric material 20 and the gate material 22. Thedielectric material 26 can be an oxide material, acting as isolationstructures between the adjacent structures 10′, as well as separating alater formed source or drain region from the gate structure, e.g., thegate dielectric material 20 and the gate material 22. The dielectricmaterial 26 can be formed by a conventional deposition process (e.g.,CVD), followed by a planarization process. In embodiments, theplanarization process will expose top surfaces of the fins 16, e.g.,semiconductor material.

In FIG. 6, a wide (thick) portion of semiconductor material 16 c isformed on the fin 16 by an epitaxial growth process. As should beunderstood by those of skill in the art, the wide portion 16 c can beused as a source or drain region of the structure 10′; whereas, the wideportion 16 a can be used as a drain or source region of the structure10′, respectively. The dielectric material 20 and the gate material 22will wrap around the vertical sidewalls of the fins 16, between thewider portions 16 a, 16 c.

Referring now to FIGS. 7 and 8, contact openings 28 are formed in thedielectric material 26, in order to form silicide regions 16 a′ and 16c′ on the source and drain contact regions of the gate structure 10′. Inembodiments, the openings 28 are formed by conventional lithography andetching processes, e.g., reactive ion etching (RIE) processes. Thesilicide regions 16 a′ and 16 c′ can be formed by a platinum silicideprocess; although cobalt and nickel silicide processes are alsocontemplated by the present invention.

As should be understood by those of skill in the art, the silicideprocess begins with deposition of a thin transition metal layer, e.g.,platinum, cobalt or nickel, over fully formed and patternedsemiconductor devices (e.g., doped or ion implanted source and drainregions formed from the wide portions 16 a, 16 c as should be understoodby those of skill in the art). After deposition of the material, thestructure is heated allowing the transition metal to react with exposedsilicon (or other semiconductor material as described herein) in theactive regions of the semiconductor device (e.g., source, drain, gatecontact region) forming a low-resistance transition metal silicide.Following the reaction, any remaining transition metal is removed bychemical etching, leaving silicide contacts 16 a′ and 16 c′ in theactive regions of the device.

FIG. 8 shows a cross-sectional view of a single device 10′. In FIG. 8,the drain contact 30, the gate contact 32 and the source contact 34 areformed through the openings. The contacts 30, 32, 34 are formed by ametal deposition process, in direct electrical contact with therespective silicide regions 16 a′ and 16 c′ and on metal gate materialdeposited on the gate structure. The contacts 30, 32, 34 can be formedby a metal deposition process, with liner material. For example, thecontacts can be tungsten or copper or alloys thereof, with the linermaterial being TiN or TaN; although other materials are alsocontemplated by the present invention.

In embodiments, the metal material can be formed by a conventionaldeposition process, e.g., CVD, followed by a planarization process toremove any excessive material from the surface of the dielectricmaterial 26. Following the metal fill process to form the contacts 30,32, 34, additional dielectric material 26′ is formed on the structure,e.g., over the devices 10′, followed by a planarization process toexpose portions of the contacts 30, 32, 34 for middle of the line (MOL)and back end of the line (BEOL) processes. In embodiments, thedielectric material 26, 26′ can be an oxide material or ultra low-kdielectric material, as examples. As should now be understood by thoseof skill in the art, by implementing the processes of the presentinvention, e.g., moving the contact to the ends of the structures, theresultant pitch of adjacent devices 10′ can now be scaled significantly,e.g., 6 nm or less.

FIGS. 9a and 9b show a cross-sectional view and a top down view of analternative structure 10″, after formation of the additional dielectricmaterial 26′. In embodiments, the deposition of the additionaldielectric material 26′ will form an air gap 36 between adjacent devices10″, effectively reducing the contact resistance. (This air gap 36 canalso be formed with the process flow of FIG. 8.) The formation of theair gap 36 is due to a pinching effect of the deposition process,between the minimum pitch, e.g., spacing, of the adjacent devices 10″.

In addition, the devices 10″ shown in FIGS. 9a and 9b include a sharedcontact strap 32′ formed at the drain regions of the devices (FETs) 10″.It should be understood by those of skill in the art that the sharedcontact strap 32′ can equally be formed at the source regions, e.g.,other end of the device 10″, or both the source and drain regions asschematically represented by FIGS. 9a and 9b . Thus, the presentinvention contemplates shared or individual S/D silicide and contactregions. Also, in each of the embodiments described herein, the channelcurrent is in a vertical direction, as these devices are vertical FETs.

FIGS. 10a and 10b show a cross-sectional view and a top down view ofalternative devices 10′″ and respective processing steps in accordancewith aspects of the present invention. These alternative devices 10′″include merged regions 40, e.g., bottom merged drain region, oralternatively a merged source region or both a source region and a drainregion. As should be understood, these merged devices 10′″ provide evenlower resistance between adjacent FETs; compared to a non-merged FET.The merged devices 10′″ can be formed using the processes describedherein, with the merged regions 40 being formed together during theformation of the fins structures (and subsequent ion implantation ordoping of the source/drain regions), instead of separately for separatedevices. A contact 40′ also spans across the merged region 40. Thecontact 40′ is formed by conventional lithography, etching anddeposition processes as already described herein including the silicideand contact formation. In embodiments, an air gap 36 can optionally beformed between the devices 10′″, as already described herein.

FIGS. 11a and 11b show a cross-sectional view and a top down view ofalternative devices 10″″ and respective processing steps in accordancewith aspects of the present invention. These alternative devices 10″″are single sided gates, as shown representatively by the metal material22′ and dielectric material 20′ provided on only a single side of thefin structures 16. These devices 10″″ also include an optional mergeddrain region 40 and contact 40′, resulting in lower resistance andhigher capacitance. In embodiments, the drain region 40 and contact 40′of the devices 10″″ can be representative of a merged source region, orboth a source and a drain region. In embodiments, an air gap 36 canoptionally be formed between the devices 10″″, as already describedherein.

FIG. 12 shows another alterative structure and respective processingsteps. In this alternative structure, the devices 10′″″ include gatematerial 22 and dielectric material 20 wrapping around two finstructures 16′ (in parallel). In embodiments, the gate material 22 anddielectric material 20 can be deposited and patterned in the sameprocessing steps to form the gate structures spanning over the two finstructures 16′. Also, an air gap 36 can optionally be formed betweenadjacent devices 10′″″, extending along the two fin structures 16′, asalready described herein.

Moreover, the devices 10′″″ include a merged bottom drain region 60, oralternatively a source region or both a source region and a drainregion, thereby resulting in lower resistance and higher capacitance.The alternative devices 10′″″ also can include a shared contact strap asshown by reference numeral 60, formed using the processes describedherein and as should understood by those of ordinary skill in the artsuch that no further explanation is needed for an understanding of thepresent invention.

The method(s) as described above is used in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips can bedistributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed:
 1. A method of forming a semiconductor structure,comprising: forming two vertical fin structures of semiconductormaterial, wherein the drain regions of the two vertical fin structuresare merged together and share a single contact; and the source regionsof the two vertical fin structures are unmerged and have separatecontacts.
 2. The method of forming a semiconductor structure of claim 1,further comprising forming gate material contacting with the twovertical fin structures.
 3. The method of forming a semiconductorstructure of claim 2, wherein: the gate material includes a gatedielectric material and a metal material on the two vertical finstructures, with a space between the two vertical fin structures.
 4. Themethod of forming a semiconductor structure of claim 3, wherein the gatematerial is entirely around a vertical extent of the two vertical finstructures.
 5. The method of forming a semiconductor structure of claim3, wherein the gate material is on a single side of a vertical extent ofthe two vertical fin structures.
 6. The method of forming asemiconductor structure of claim 1, further comprising forming an airgap between the two vertical fin structures.
 7. The method of forming asemiconductor structure of claim 1, further comprising forming aninterlevel dielectric between the two vertical fin structures.
 8. Themethod of forming a semiconductor structure of claim 1, furthercomprising forming an air gap in an interlevel dielectric between thetwo vertical fin structures.
 9. The method of forming a semiconductorstructure of claim 1, wherein the source region and drain region of thetwo vertical fin structures comprises a first dimension and epitaxiallygrown semiconductor material on a portion above the first dimension. 10.The method of forming a semiconductor structure of claim 1, furthercomprising forming gate material contacting with the two vertical finstructures, wherein the gate material includes a gate dielectricmaterial and a metal material on the portion of the two vertical finstructures.
 11. A method of forming a semiconductor structurecomprising: forming two vertical fin structures of semiconductormaterial with a source region and a drain region at opposing ends;forming gate material about the two adjacent fin structures and betweenthe opposing ends; and forming an air gap in an interlevel dielectricbetween the two vertical fin structures, wherein the drain regions ofthe two vertical fin structures are merged together and share a singlecontact; and the source regions of the two vertical fin structures areunmerged and have separate contacts.
 12. A method of forming asemiconductor structure comprising: forming two vertical fin structuresof semiconductor material with a source region and a drain region atopposing ends; forming gate material about the two adjacent finstructures and between the opposing ends; and forming an air gap in aninterlevel dielectric between the two vertical fin structures, wherein:the source region and the drain region of the two vertical finstructures comprises a first dimension and epitaxially grownsemiconductor material on a narrow portion above the first dimension;and drain contacts and source contacts at opposing ends of the twovertical fin structures comprise silicide regions and metal material onthe silicide regions.
 13. The method of forming a semiconductorstructure of claim 12, wherein the gate material includes a gatedielectric material and a metal material on the narrow portion of thetwo vertical fin structures.
 14. The method of forming a semiconductorstructure of claim 12, wherein at least one of the drain region and thesource region of the two vertical fin structures are merged together.15. The method of forming a semiconductor structure of claim 12, whereinat least one of the drain region and the source region of the twovertical fin structures are connected together by a conductive strap.16. The method of forming a semiconductor structure of claim 12, whereinthe gate material is entirely around a vertical extent of at least oneof the two vertical fin structures.
 17. The method of forming asemiconductor structure of claim 12, wherein the gate material is on asingle side of a vertical extent of at least one of the two vertical finstructures.
 18. The method of forming a semiconductor structure of claim12, wherein the drain region and the source region of the two verticalfin structures which are merged together and are connected together by aconductive strap.